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Zoology Publications from Victoria University of Wellington—Nos. 54 to 57

Identification of Heptranchias dakini as H. perlo

Identification of Heptranchias dakini as H. perlo

Whitley (1931, p. 310) gave three diagnostic characters for H. dakini. The first of these was that the head was "4 ½ in total length", but Whitley did not say how this differed from the situation in H. perlo. From our data (Table 1) we find no obvious difference in head length (measured to the posterior end of the 7th gill-opening) relative to total length between Australian, New Zealand and Atlantic Heptranchias. Nor do we find any specimens in which this proportion is 4½. The range for three Australian specimens, including the two "Types" of dakini, is 5.0 to 5.5 (mean 5.3); for 15 New Zealand specimens 4.8 to 5.6 (mean 5.2); and for two Cuban specimens the almost equivalent prepectoral lengths, as given by Bigelow and Schroeder, equal 4.8 and 5.2 in total length. We note that McCulloch's illustration shows a head length of about 4.5 in total length and assume that this was the basis of Whitley's statement.

Whitley's second diagnostic character for H. dakini was that the anal fin originates below the middle of the dorsal fin base. We have examined this character and find that it occurs only in females; it is present in New Zealand specimens and in a Cuban specimen of H. perlo as well as in Australian specimens. Males on the other hand have the anal fin origin further rearward, below the posterior end of the dorsal base or at least nearer to that level than to the middle of the dorsal base. There is some overlap between the sexes, with a minority of the females approaching or overlapping the male condition. Table 1 shows for each of our specimens the proportion (%) of the dorsal fin base which is anterior to the anal fin origin. In 13 of the 17 females there is from 50.0% to 71.7% of the dorsal base anterior to the anal fin origin. In other words, in these 13 females the anal fin origin is nearer to the middle of the dorsal base than to the posterior end. In the remaining four females there is from 75.4% to 100.0% of the dorsal base anterior; thus their anal fin origin is nearer to the posterior end of the dorsal fin base than to the middle. The condition in these four females is similar to that of the five males in which from 76.3% to 102.8% of the dorsal base is anterior.

It is clear from the above data that the position of the anal fin relative to the dorsal fin in Heptranchias predominantly reflects sexual dimorphism and offers no evidence for distinguishing a separate Australian species, H. dakini, from the world-wide H. perlo.

It is, perhaps, surprising that this possibility did not occur to Whitley when he described H. dakini, insofar as the "Types" of H. dakini which he designated (Whitley, 1957) included a male as well as a female specimen—and these particular specimens differ strongly in this feature.

Whitley's third diagnostic criterion for H. dakini was that the anal base is shorter than the dorsal base. We find that this is true for the Australian H. dakini material, but it also applies to our New Zealand specimens, as well as to the page 5Atlantic specimens of H. perlo described in Bigelow and Schroeder (1948, p. 89). There seems, therefore, to be no substance in this criterion for recognising H. dakini.

On the basis of the above data we regard H. dakini as conspecific with H. perlo.

Because there are relatively few published measurements of H. perlo we provide here (Table 2) measurements of five New Zealand specimens and three Australian specimens, plus two Cuban specimens (from Bigelow and Schroeder, 1948).

In the same table we give vertebral counts of six Australian and New Zealand specimens, which range from 90–93 precaudal and 52–59 caudal centra. Such counts closely agree with those published in Springer and Garrick (1964, p.83) for three western North Atlantic specimens (89–90 precaudal, 52–61 caudal) of H. perlo and provide supporting evidence that only one species is involved.